Wasps or mice in your compost pile?

Recently Green Action Centre has been receiving calls from people who complain that they have unwelcome visitors living in their compost pile. While the solution to getting rid of these little pests is not always simple, the solution to keeping them out in the first place is.

Generally the existence of mice/vole or wasp nests is an indicator that your compost pile is too dry. With the heat and lack of precipitation we have been experiencing this summer, it is not surprising that compost piles are dry. Remember that your compost pile should be about as damp as a rung out sponge. You also likely need to stir or turn the pile to ensure that the moisture is distributed throughout. If the pile is moist and aerated, it will build up the kind of heat that will make it an inhospitable environment for mice and wasps.

I recently came back from a few weeks of holidays only to find wasps were just beginning to set up shop in my compost pile. I wet the pile down, left it overnight (hoping to avoid getting stung) and then turned the pile. Wasps gone!

If wasps have however settled in for the long haul, you may have to explore other options. I would still recommend that the first order of business be to wet the pile down and leave it for a few days. To reduce the risk of getting stung, do this at night when the wasps are less active. Wetting your pile may get it heating up again and convince the wasps to leave, however I wouldn’t hold my breath. If they seem to give up residence, then you can stir the pile and go back to normal. Normal of course means monitoring the pile a bit more often to make sure it does not get too dry and stirring it from time to time. If they don’t, unless you have a bee keeper’s suit or similar protection, you may have to wait until late fall when they die off and then stirring the pile thoroughly.

Mice or voles present a different and sometimes more difficult problem. They won’t sting you, but they definitely can leave you squeamish. I have been composting for over 20 years in Charleswood. My cat brings mice home regularly and leaves them as a gift for me on the deck or patio, but I have never had them in my compost pile. Keeping the pile working (hot) is the key. If they need air conditioning to keep their home cool, they will leave and find another place that is naturally cooler.

Here are some other ideas on getting rid of these little critters:

Aerating the pile thoroughly each day for 3 or 4 days will disturb the nest and make residency less desirable.

The mice or voles may be burrowing under your bin so look for any tunnels around the edges and flood them with water. They will collapse but if they reappear again keep flooding them.

Avoid the use of poisons as they can also be ingested by pets.

Another option for keeping mice out of your pile is to Pest Proof it. If you have a molded plastic bin you could place ¼ inch wire mesh under the bin to keep them from tunneling in. You will want to wrap the wire over the bottom lip of the bin as well as make sure that it is on level ground and pinned down solidly. If you have a wood bin pest proofing is a bit more difficult. You can line your bin with a similar mesh and make a mesh lid, however gaps in the mesh at corners can be an issue. Click here for details on pest proofing your wood bin.

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14 Comments

Barbara
on December 12, 2017 at 2:57 pm

My backyard neighbor has created a compost of yard materials on the edge of their property adjacent to my property. The compost pile is approximately 25’ from their house.

I don’t want to deal with the smells or unwelcome critters Are their any guidelines or ordinances that could require my neighbor to move their compost further away from our joint property line? Thanks

It’s hard to give you a proper answer without knowing where you live, but assuming that you’re in Winnipeg, here it is:

Compost, properly managed, shouldn’t be producing any smells or attracting any pests beyond what is already present in the area. Having it properly turned, watered, and covered in browns are key for this, as well as avoiding adding any meat, dairy, bones, or oils.

If their compost is on their property, they are fully within their rights to have and maintain the pile. If you’re concerned, I recommend that you come pick up one of our Backyard Composting pamphlets or brochures and perhaps slip it into their mailbox with a note letting them know about our composting InfoLine. As well, you may wish to partner up with them as many backyard compost owners are happy to let their neighbours deposit extra food scraps and yard waste if they have the space – you could really reduce your own waste footprint by following the good example of your neighbours!

If you are currently having active issues with smells or pests (unlikely as it’s cold out), that needs to first be addressed neighbour-to-neighbour and if that fails, you can turn to calling 311 to see how the City deals with neighbourly disputes. However, they significantly prefer that you resolve it between yourselves.

I know I am years behind so I will be surprised to get an answer but….I live in Wisconsin and it’s getting cold. I discovered nice in my compost and am concerned that adding moisture will create a frozen effect. What can you offer me for advice? I just turned it and added moist leaves and I will turn it again for the next few days but what about the hole I found?

I wouldn’t be too concerned about adding a bit of moisture to your pile. I might freeze later in the winter but there will still be lots of activity in your pile at this time. There are some organisms that remain active even in freezing temperatures and lets not forget that in the middle of the pile it will be warmer than around the edges. If you dig down into your pile you will likely find it is still warm.
Turning the pile and disturbing the nest will certainly help to deter them as well. You might want to add some water as your turn and so that you can get the bottom of the pile (likely where they are nesting) damp as well.

I love the mice in the compost bin. They dig tunnels to let in the air. A cardboard tent to keep out the extra rain did work as a mouse control as I found mouse dead from the gas build up. This happened three times so it works.

Sorry for the late response Charlotte. The compost will not be contaminated and you can certainly use it. That said, the first priority is to get the mice to find a new home. Then you want to make sure that the conditions that created a the problem in the first place are changed.
I suspect that the main issue is that the pile is dry and and so it created a nice home for the mice to just burrow into. Make sure that you keep the pile about a damp as wrung out sponge and it will start to heat up again and make it too warm for the mice. As it indicates above, aerating the pile thoroughly each day for 3 or 4 days will disturb the nest and they will likely move on. After that make sure that you keep the pile damp and aerate once in a while so that you don’t once again create a nice home for the mice.
If you have questions or would like clarification, please feel free to call 925-3776.

We received some feedback from one of the individuals that called us about wasps in her compost pile and wetting down the pile, waiting a day, and then stirring things up worked. No wasps and no stings!

I don’t yet have either mice or wasps, but I was inspired by your article to check my compost bins and and pile. I have been wetting down the tops of them, assuming that the water would seep down. I was really shocked to find how dry the compost was at the bottom and around the sides. This hot dry weather just sucks the moisture out. Thanks for the heads up.